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Astronomical Applications Department, U.S. Naval Observatory - NOVAS 2004 Overview (Page 13)

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Astronomical Applications Department, U.S. Naval Observatory - NOVAS 2004 Overview
FUNARG ­ now evaluates Simon et al. (1994) expressions for the fundamental solar and lunar
arguments. However, IERS subroutine NU2000A, that evaluates the full nutation series, develops
its fundamental arguments internally (a mixed bag of expressions).
WOBBLE ­ very tiny (inconsequential for most applications) rotation about z axis added to matrix to
correct ITRS longitude origin to TEO, using recently published approximation to TEO longitude
as a function of time (which requires the new time argument to this subroutine). Essentially, this
changes W rotation to W'. Also changed matrix element expressions from first-order
approximations to exact expressions for increased precision.

Other Internal Code Changes
Many minor changes have been made in the code. Obviously many of the comment statements had to
be revised, and others added, too numerous to try to list. Some of the code is now more Fortran-77-
like and less Fortran-66-like, especially in the subroutines in which other changes had to be made; a
uniform scrub was not done. NOVAS still has plenty of ancient-looking code, it's still all-caps, and
there are still some GO TOs. On the other hand, since NOVAS is mostly computational, flowing top-
to-bottom, without any complicated logic, it hardly matters.
Some variable names were changed. For example, the variable PI in some subroutines was used for
the parallax and not the mathematical constant
=3.14159..., which seemed nutty. In these cases, the
variable name is now PX. The input (catalog) RA and Dec for many subroutines had been named
RAM and DECM, the M indicating "mean"; these are now RAI and DECI, the I indicating "ICRS".
Many similar trivial changes have been made.
Unfinished Business
The precession algorithm used in NOVAS version F2.9, from the IERS Conventions (2003), is a
temporary algorithm. The IAU Working Group on Precession and the Ecliptic has been charged with
recommending a dynamically consistent precession theory for use as the new IAU standard. The
working group has evaluated several candidate theories and seems to be moving toward endorsing the
Capitaine, et al. (2003) precession, also known as P03 -- but with a correction. The working group's
final recommendation is expected in mid-to-late 2004. NOVAS version F3.0 will incorporate the new
IAU precession theory as recommended by the working group, but will not be made public until the
working group's final report has been accepted for publication (this whole topic has had too many
examples of last-minute "adjustments"). Meanwhile, NOVAS version F2.9 will be used for the U.S.
sections of the 2006 Astronomical Almanac.

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NOVAS 2006 Overview, thesis, Ranson,

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